1. Field of the Invention
This invention relates to improvements in a shock absorbing belt for a child, of a seat belt restraint system (for a child or of a child seat) arranged to protect a child occupant in an automotive vehicle, an airplane, or the like, when the occupant is subjected to an impact during a high speed cruising, or a collision of the vehicle, or falling of the airplane.
2. Description of the Prior Art
Hitherto seat belt restraint systems as protecting devices for an occupant have been known in the field of automotive vehicles and airplanes. A typical seat belt restraint system will be discussed with reference to FIG. 4 which shows the fabric structure of a seat belt forming part of the system. The fabric structure is woven by interlacing warp yarns 2 and weft yarns as base yarns. The fabric structure of FIG. 4 is of a 2/2 twill weave, and may be of a 4/4 twill weave.
In an example of such a seat belt for an adult, the warp yarns have a size of 1000 to 1500 D, a breaking strength of 8 to 10 g/D, and an elongation percentage of 10 to 20%. Additionally, the weft yarns have a size of 500 to 750 D, a breaking strength of 5 to 7 g/D, and an elongation percentage of 15 to 25%.
Now, recently energy absorbing belts for absorbing impact have been proposed as disclosed in Japanese Patent Publication No. 54-20732 and Japanese Patent Provisional Publication No. 60-261474. The energy absorbing belt, as disclosed in Japanese Patent Publication No. 54-20732, uses two different kinds of warp yarns, in which at least one of the two kinds of the warp yarns is formed of an aromatic polyamide fiber or an aromatic polyhydrazide-polyamide copolymer fiber. The energy absorbing belt, as disclosed in Japanese Patent Provisional Publication No. 60-261474 uses a kind of additional yarns in addition to base yarns, so the base yarns largely deform as compared with the additional yarns when the same force is applied to the base yarns and the additional yarns. Thus, the above energy absorbing belts are arranged to plastically deform when they absorb an impact energy.
However, drawbacks have been encountered in the above discussed conventional seat belts or energy absorbing belts as set forth below.
Concerning the above-mentioned conventional seat belt for an adult, although the seat belt has a low elongation percentage of 3 to 8% in its longitudinal direction, the timing of an initial restraint for an occupant is unavoidably retarded because a drawing-out action of the seat belt occurs after stopping of rotation (for drawing out the belt) of a belt winding-up shaft of a seat belt retractor. As a result, the occupant cannot be sufficiently restrained and protected from a secondary collision.
Additionally, as seen in FIG. 5, which shows load-elongation characteristics of the conventional seat belt formed of polyester fiber, the primary rise of a load-elongation curve is gentle, and therefore, the timing of the initial restraint of the occupant is retarded, thereby making it impossible to sufficiently restrain and protect the occupant. Additionally, although an outlet locking mechanism has been proposed to prevent the above-mentioned drawing-out action of the seat belt from the retractor, the mechanism is expensive and provides the possibility of the belt being broken.
Concerning the above-mentioned energy absorbing belt, as disclosed in Japanese Patent Provisional Publication No. 54-20732, the warp yarns constituting the belt include a kind of warp yarns, that are woven in tile fabric structure so-called to have a so-called weaving shrinkage percentage less than that of another kind of warp yarns, which are also woven in the fabric structure. The primary rise in the load-elongation characteristics of the belt can be obtained by the warp yarns having the less weaving shrinkage percentage; however, the warp yarns are woven in, and therefore, unavoidably elongate though they are less in the weaving shrinkage percentage. Therefore, this energy absorbing belt has a such a defect that the timing of the primary rise or initial restraint for the occupant is unavoidably retarded, which makes it impossible to reduce a head injury criteria (HIC) according to FMVSS No. 208.
Concerning the above-mentioned energy absorbing belt, as disclosed in Japanese Patent Provisional Publication No. 60-261474, base materials (yarns) and additional materials (yarns) constituting the fabric structure of the belt are, respectively, provided with different elongation characteristics under a mechanical pretreatment and/or a pretreatment with a heating device, made at the time of interlacing them with each other. The mechanical pretreatment is accomplished to set the yarns at a predetermined elongation percentage value by application of elongation, contraction and/or twist to the yarns. The treatment with the heating device is accomplished by elongating the yarns in a hot condition, then contracting them, and thereafter cooling them.
Accordingly, this energy absorbing belt cannot be produced without troublesome processes thereby making difficult production thereof, and thus, raising a production cost thereof. Additionally, this energy absorbing belt is inferior in the characteristics of the initial restraint for the occupant, and insufficient in energy absorbing effect thereby making it difficult to sufficiently soften an impact applied to the vehicle occupant during a vehicle collision.
It is to be noted that the above-discussed seat belt and energy absorbing belts are used for adult occupants, and therefore, poor in energy absorbing ability for children who are light in weight so as to be low in reduction effect for the head injury criteria (HIC) at a vehicle collision or the like.